At the outset of a drilling operation, drillers typically establish a drilling plan that includes a target location and a drilling path, or well plan, to the target location. Once drilling commences, the bottom hole assembly (“BHA”) is directed or “steered” from a vertical drilling path in any number of directions, to follow the proposed well plan. For example, to recover an underground hydrocarbon deposit, a well plan might include a vertical section to a point above the reservoir, then a directional section and deviated or horizontal section that penetrates the deposit. The drilling operator may then steer the BHA, including the bit, through the vertical, directional and horizontal aspects in accordance with the plan.
In some embodiments, directional control of the BHA can be via a “push-the-bit” method, which involves applying to the bit a radial force which is designed to drive the bit to drill at a certain deviation in a desired direction in relation to the center axis of the bit. Direction and deflection can be adjusted continuously, even whilst the drilling string rotates. Conventionally, and when a drilling operator provides instructions to the BHA and other drilling equipment, the drilling operator draws on his or her past experiences and the performance of the well to create the instructions based on conditions in the well and/or historical performance of the current well or similar wells. This is a very subjective process that is performed by the drilling operator and that is based on his or her judgment. In some instances, the creation of the instructions by the drilling operator is not optimal. As a result, any one or more is a result: the tortuosity of the actual well path is increased, which increases the difficulty of running downhole tools through the wellbore and increases the likelihood of damaging any future casing that is installed in the wellbore; and the actual drilling path differs significantly from the well plan. Moreover, the time required for the BHA to relay data from the BHA to the surface, for the drilling operator to review the data and create new instructions, and for the instructions to be relayed back down to the BHA, results in further deviation from the target well path. Thus, a method and apparatus for the BHA and/or drilling rig to automatically create instructions is needed.